Ten genotypes of cowpea were grown in four environments comprising the early and late seasons of Ogbomoso and Abeokuta locations in 2005 and 2006. Joint linear regression analysis indicated the presence of Genotype x Environment interaction even though, a proportion was non-linear. The differences in the values of the regression coefficient and the correlation of grain yield revealed that the genotypes responded differently to the environments and that regression coefficient as a technique could not be used to identify genotype performance in specific locations. The use of Deviation mean square and Ecovalence mean square techniques produced similar results on the consistency of genotypes performance hence, Deviation mean square and Ecovalence mean square may not be simultaneously used. However, regression coefficient, Si3, Pi, and Modified rank sum techniques can be jointly used to select genotypes based on their yielding ability and response to environmental changes.
Key words: Genotype X environment interaction, selection techniques, cowpea, Vigna unguiculata.
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